Environmental control system utilizing two pass secondary heat exchanger and cabin pressure assist

ABSTRACT

A system of an aircraft includes an inlet arranged in fluid communication with a bleed air source such that the inlet is configured to receive a flow of bleed air. A compressing device includes a compressor having a compressor inlet fluidly connected to the inlet. A heat exchanger is fluidly coupled to an outlet of the compressor. The heat exchanger includes a first pass and a second pass, both of which are located downstream from the compressor. An outlet of the first pass is directly connected to an inlet of the second pass via a first conduit. The outlet of the first pass is also fluidly connected to an inlet of the compressor via a second conduit such that a portion of the bleed air output from the first pass is returned to the compressor inlet via the second conduit.

BACKGROUND

In general, with respect to present air conditioning systems ofaircraft, cabin pressurization and cooling is powered by engine bleedpressures at cruise. For example, pressurized air from an engine of theaircraft is provided to a cabin through a series of systems that alterthe temperatures and pressures of the pressurized air. To power thispreparation of the pressurized air, the only source of energy is thepressure of the air itself. As a result, the present air conditioningsystems have always required relatively high pressures at cruise.Unfortunately, in view of an overarching trend in the aerospace industrytowards more efficient aircraft, the relatively high pressures providelimited efficiency with respect to engine fuel burn.

SUMMARY

According to one embodiment, a system is provided. The system includesan inlet providing a first medium; a compressing device comprising acompressor, and at least one heat exchanger located downstream of thecompressor. The compressing device is in communication with the inletproviding the first medium. The at least one heat exchanger includes afirst pass and a second pass. An outlet of the first pass of the atleast one heat exchanger is in fluid communication with an inlet of thecompressor.

Additional features and advantages are realized through the techniquesof the embodiments herein. Other embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed invention. For a better understanding of the invention withthe advantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a diagram of an schematic of an environmental control systemaccording to an embodiment;

FIG. 2 is operation example of an environmental control system accordingto an embodiment; and

FIG. 3 is operation example of an environmental control system accordingto another embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the FIGS.

Embodiments herein provide an environmental control system that utilizesa two pass heat exchanger patent that includes quench loop andrecirculation air mixed in between the two passes to leverage lowerpressure engine bleed air to provide cabin pressurization and cooling ata high engine fuel burn efficiency.

In general, embodiments of the environmental control system may includeone or more heat exchangers and a compressing device. A medium, bledfrom a low-pressure location of an engine, flows through the one or moreheat exchangers into a chamber. Turning now to FIG. 1, a system 100 thatreceives a medium from an inlet 101 and provides a conditioned form ofthe medium to a chamber 102 is illustrated. The system 100 comprises acompressing device 120 and a heat exchanger 130. The elements of thesystem are connected via valves, tubes, pipes, and the like. Valves aredevices that regulate, direct, and/or control a flow of a medium byopening, closing, or partially obstructing various passageways withinthe tubes, pipes, etc. of the system 100. Valves can be operated byactuators, such that flow rates of the medium in any portion of thesystem 100 can be regulated to a desired value.

As shown in FIG. 1, a medium can flow from an inlet 101 through thesystem 100 to a chamber 102, as indicated by solid-lined arrows A, B. Inthe system 100, the medium can flow through the compressing device 120,through the heat exchanger 130, from the compressing device 120 to theheat exchanger 130, from the heat exchanger 130 to the compressingdevice 120, etc. Further, the medium can recirculate from the chamber102 to the system 100, as indicated by the dot-dashed lined arrow D (andcan then flow back to the chamber 102 and/or external to the system100).

The medium, in general, can be air, while other examples include gases,liquids, fluidized solids, or slurries. When the medium is beingprovided from the chamber 102 of the system 100, the medium is referredto herein as recirculated air. When the medium is being provided by anengine connected to the system 100, such as from the inlet 101, themedium can be referred to herein as bleed air. With respect to bleedair, a low-pressure location of the engine (or an auxiliary power unit)can be utilized to provide the medium at an initial pressure level neara pressure of the medium once it is in the chamber 102 (e.g., chamberpressure, also referred to as cabin pressure in the aircraft example).

For instance, continuing with the aircraft example above, air can besupplied to the environmental control system by being “bled” from acompressor stage of a turbine engine. The temperature, humidity, andpressure of this bleed air varies widely depending upon a compressorstage and a revolutions per minute of the turbine engine. Since alow-pressure location of the engine is utilized, the air may be slightlyabove or slightly below cabin pressure (e.g., the pressure in thechamber 102). Bleeding the air at such a low pressure from thelow-pressure location causes less of a fuel burn than bleeding air froma higher pressure location. Yet, because the air is starting at thisrelatively low initial pressure level and because a drop in pressureoccurs over the one or more heat exchangers, a pressure of the air maydrop below the cabin pressure while the air is flowing through the heatexchanger 130. When the pressure of the air is below the cabin pressure,the air will not flow into the chamber to provide pressurization andtemperature conditioning. To achieve the desired pressure, the bleed-aircan be compressed as it is passed through the compressing device 120.

The compressing device 120 is a mechanical device that controls andmanipulates the medium (e.g., increasing the pressure of bleed air).Examples of a compressing device 120 include an air cycle machine, athree-wheel machine, a four wheel-machine, etc. The compressing caninclude a compressor, such as a centrifugal, a diagonal or mixed-flow,axial-flow, reciprocating, ionic liquid piston, rotary screw, rotaryvane, scroll, diaphragm, air bubble compressors, etc. Further,compressors can be driven by a motor or the medium (e.g., bleed air,chamber discharge air, and/or recirculation air) via a turbine.

The heat exchanger 130 is a device built for efficient heat transferfrom one medium to another. Examples of heat exchangers include doublepipe, shell and tube, plate, plate and shell, adiabatic wheel, platefin, pillow plate, and fluid heat exchangers., air forced by a fan(e.g., via push or pull methods) can be blown across the heat exchangerat a variable cooling airflow to control a final air temperature of thebleed air.

The system 100 of FIG. 1 will now be described with reference to FIG. 2,in view of the aircraft example. FIG. 2 depicts a schematic of a system200 (e.g., an embodiment of system 100) as it could be installed on anaircraft.

The system 200 will now be describe with respect to a conventional bleedair driven environmental control system of an airplane utilizing acontemporary cabin three-wheel air conditioning system. The conventionalbleed air driven air environmental control system receives bleed air ata pressure between 30 psia (e.g., during cruise) and 45 psia (e.g., onthe ground). In the conventional bleed air driven air environmentalcontrol system, during hot day ground operation, the centrifugalcompressor of the air cycle machine receives nearly all of the flow ofthe bleed air at a pressure of approximately 45 psia. Further, duringhot day cruise operation, the centrifugal compressor of the air cyclemachine receives only a portion of the flow of the bleed air at apressure of 30 psia. The remainder of the bleed air bypasses thecentrifugal compressor via the air cycle machine bypass valve and issent to the cabin.

In contrast to the conventional bleed air driven environmental controlsystem utilizing the contemporary cabin three-wheel air conditioningsystem, the system 200 is an example of an environmental control systemof an aircraft that provides air supply, thermal control, and cabinpressurization for the crew and passengers of the aircraft at a highengine fuel burn efficiency. The system 200 illustrates bleed airflowing in at inlet 201 (e.g., off an engine of an aircraft at aninitial flow rate, pressure, temperature, and humidity), which in turnis provided to a chamber 202 (e.g., cabin, flight deck, pressurizedvolume, etc.) at a final flow rate, pressure, temperature, and humidity.The bleed air can recirculate back through the system 200 from thechamber 202 (herein cabin discharge air and recirculated air, which inFIG. 2 are represented by the dot-dashed lines D1 and D2, respectively)to drive and/or assist the system 200.

The system in includes a shell 210 for receiving and directing ram airthrough the system 200. Note that based on the embodiment, an exhaustfrom the system 200 can be sent to an outlet (e.g., releases to ambientair through the shell 210).

The system 200 further illustrates valves V1-V8, a heat exchanger 220,an air cycle machine 240 (that includes a turbine 243, a compressor 244,a turbine 245, a fan 248, and a shaft 249), a condenser 260, a waterextractor 270, and a recirculation fan 280, each of which is connectedvia tubes, pipes, and the like. Note that the heat exchanger 220 is anexample of the heat exchanger 130 as described above. Further, in anembodiment, the heat exchanger 220 is a secondary heat exchanger that isdownstream of a primary heat exchanger (not shown). Note also that theair cycle machine 240 is an example of the compressing device 120 asdescribed above.

The air cycle machine 240 extracts work from the medium or performs workon the medium by raising and/or lowering pressure and by raising and/orlowering temperature. The compressor 244 is a mechanical device thatraises the pressure of the bleed-air received from the inlet 201. Theturbines 243, 245 are mechanical devices that drive the compressor 244and the fan 248 via the shaft 249. The fan 248 is a mechanical devicethat can force via push or pull methods air through the shell 210 acrossthe secondary heat exchanger 220 at a variable cooling airflow. Thus,the turbines 243, 245, the compressor 244, and the fan 248 togetherillustrate, for example, that the air cycle machine 240 may operate as afour-wheel air cycle machine that utilizes air recirculated ordischarged from the chamber 202 (e.g., in an embodiment, the air cyclemachine 240 utilizes the chamber discharge air to perform compressingoperations, as indicated by dot-dashed line D1.)

The condenser 260 is particular type of heat exchanger. The waterextractor 270 is a mechanical device that performs a process of takingwater from any source, such as bleed-air, either temporarily orpermanently. The recirculation fan 280 is a mechanical device that canforce via a push method air recirculation into the system 200, asindicated by dot-dashed arrow D2.

In a high pressure mode of operation of the system 200, high-pressurehigh-temperature air is received from the inlet 201 through the valveV1. The high-pressure high-temperature air enters the compressor 244.The compressor 244 pressurizes the high-pressure high-temperature and inthe process heats it. This air then enters a first pass of the heatexchanger 220 and is cooled by ram air. The air exiting the first passof the heat exchanger 220 then enters the second pass of the heatexchanger 220 to produce cool high pressure air. This cool high pressureair enters through the valve V7 into the condenser 260 and the waterextractor 270, where the air is cooled and the moisture removed. Thecool high pressure air enters the turbine 243, where it is expanded andwork extracted. The work from the turbine 243 can drive both thecompressor 244 and the fan 248. The fan 248 is used to pull a ram airflow through the heat exchanger 220. Also, by expanding and extractingwork on the cool high pressure air, the turbine 243 produces cold bleedair. After leaving the turbine 243, the cold bleed air is mixed at amixing point with the recirculation air D2 provided by the fan 280through from the valves V6 and V8. The mixing point in this case can bedownstream of the compressing device 240. This mixing point can also bereferred to as downstream of the compressor 244 and downstream of theturbine 243. By mixing the cold bleed air with the recirculation air D2,the system 200 utilizes the recirculation air, which is warm and moist,to level out the cold bleed air (e.g., raise the temperature). Thisleveled out bleed air, in turn, enters a low pressure side of thecondenser 260, cools the bleed air on the high pressure side of thecondenser 260, and is sent to condition the chamber 202.

Note that when operating in the high pressure mode, it is possible forthe air leaving the compressor 244 to exceed an auto-ignitiontemperature of fuel (e.g., 400 F for steady state and 450 F fortransient). In this situation, air from an outlet of a first pass of theheat exchanger 220 is ducted by the valve V2 to an inlet of thecompressor 244. This lowers an inlet temperature of the air entering theinlet of the compressor 244 and, as a result, the air leaving thecompressor 244 is below the auto-ignition temperature of fuel.

The high pressure mode of operation can be used at flight conditionswhen engine pressure is adequate to drive the cycle or when atemperature of the chamber 202 demands it. For example, conditions, suchas ground idle, taxi, take-off, climb, and hold conditions would havethe air cycle machine 240 operating in the high pressure mode. Inaddition, extreme temperature high altitude cruise conditions couldresult in the air cycle machine 240 operating in the high pressure mode.

In a low pressure mode of operation, the bleed air from the inlet 201through the valve V1 bypasses the air cycle machine 240 and directlythrough the first pass of the heat exchanger 220. Upon exiting the firstpass, the bleed air then mixes at a mixing point with the recirculationair recirculation air D2 provided by the fan 280 through the valves V6and V8 to produce mixed air. The mixing point in this case can bedownstream of the compressor 244 and/or upstream of a second pass of theheat exchanger 220. The mixed air enters the second pass of the heatexchanger 220, where it is cooled by ram air to the temperature requiredby the chamber 202 to produce cool air. The cool air then goes directlyinto the chamber 202 via the valve V7. Further, the chamber dischargeair D1 is used to keep the air cycle machine 240 turning at a minimumspeed. That is, chamber discharge air D1 flowing from the chamber 202through the valves V4 and V5 enters and expands across the turbine 245,so that work is extracted. This work is utilized to turn the air cyclemachine 240 at, for example, a minimum speed of approximately 6000 rpm.The air exiting the turbine 245 is then dumped overboard through theshell 210.

The low pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 isapproximately 1 psi above the chamber pressure (e.g., conditions atcruise where altitudes are above 30,000 ft. and conditions at or nearstandard ambient day types).

In a boost pressure mode of operation, the bleed air from the inlet 201enters the compressor 244, where it is compressed and heated. Thecompressed and heated air from the compressor 244 passes through thefirst pass of the heat exchanger 220 and then mixes at a mixing pointwith the recirculation air D2 provided by the fan 280 through the valvesV6 and V8 to produce mixed air. The mixing point in this case can bedownstream of the compressor 244 and/or upstream of a second pass of theheat exchanger 220. The mixed air enters the second pass of the heatexchanger 220, where it is cooled by ram air to the temperature requiredby the chamber 202 to produce cool air. The cool air then goes directlyinto the chamber 202 via valve V7. Further, the cabin discharge air D1is used to provide the energy to pressurize the bleed air entering thecompressor 244. That is, the chamber discharge air D1 flowing from thechamber 202 through the valves V4 and V5 enters and expands across theturbine 245, so that work is extracted. The amount of work extracted bythe turbine 245 is enough to turn the air cycle machine 240 at the speedrequired by the compressor 244 to raise a pressure of the bleed to avalue that can drive the bleed air through the heat exchanger 220 andinto the chamber 202.

The boost pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is as lowas 2.5 psi below the chamber pressure (e.g., conditions at cruise wherealtitudes are above 30,000 ft. and conditions at or near standardambient day types).

The system 100 of FIG. 1 will now be described with reference to FIG. 3,in view of the aircraft example. FIG. 3 depicts a schematic of a system300 (e.g., an embodiment of system 100) as it could be installed on anaircraft. Components of the system 300 that are similar to the system200 have been reused for ease of explanation, by using the sameidentifiers, and are not re-introduced. Alternative components of thesystem 300 include a valve V9, a reheater 350, a condenser 360, and awater extractor 370, along with an alternative path for therecirculation air denoted by the dotted-dashed line D3.

The reheater 350 and the condenser 260 are particular types of heatexchanger. The water extractor 370 is a mechanical device that performsa process of taking water from any source, such as bleed-air. Together,the reheater 350, the condenser 260, and/or the water extractor 370 cancombine to be a high pressure water separator.

In a high pressure mode of operation, high-pressure high-temperature airis received from the inlet 201 through the valve V1. The high-pressurehigh-temperature air enters the compressor 244. The compressor 244pressurizes the high-pressure high-temperature and in the process heatsit. This air then enters a first pass of the heat exchanger 220 and iscooled by ram air. The first pass of the heat exchanger 220 then entersthe second pass of the heat exchanger 220 to produce cool high pressureair. This cool high pressure air enters through the valve V7 into thereheater 350, where it is cooled; through the condenser 360, where it iscooled by air from the turbine 243; through the water extractor 370,where the moisture in the air is removed; and again into the reheater350, where the air is heated to nearly an inlet temperature at the valveV7. The warm high pressure and now dry air enters the turbine 243, whereit is expanded and work extracted. The work from the turbine 243 candrive both the compressor 244 and the fan 248. The fan 248 is used topull a ram air flow through the heat exchanger 220. After leaving theturbine 243, the cold air, typically below freezing, cools the warmmoist air in the condenser 360. Downstream of the condenser 360, thecold air leaving the air cycle machine 240 mixes at a mixing point withthe recirculation air D3 provided by the fan 280 through the valve V9 toproduce mixed air. The mixing point in this case can be downstream ofthe compressing device 240. This mixing point can also be referred to asdownstream of the compressor 244 and downstream of the turbine 243. Thismixed air then sent to condition the chamber 202.

When operating in the high pressure mode, it is possible for the airleaving the compressor 244 to exceed an auto-ignition temperature offuel (e.g., 400 F for steady state and 450 F for transient). In thissituation, air from an outlet of the first pass of the heat exchanger220 is ducted by the valve V2 to an inlet of the compressor 244. Thislowers an inlet temperature of the air entering the inlet of thecompressor 244 and, as a result, the air leaving the compressor 244 isbelow the auto-ignition temperature of fuel.

The high pressure mode of operation can be used at flight conditionswhen engine pressure is adequate to drive the cycle or when atemperature of the chamber 202 demands it. For example, conditions, suchas ground idle, taxi, take-off, climb, and hold conditions would havethe air cycle machine 240 operating in the high pressure mode. Inaddition, extreme temperature high altitude cruise conditions couldresult in the air cycle machine 240 operating in the high pressure mode.

In a low pressure mode of operation, the bleed air from the inlet 201through the valve V1 bypasses the air cycle machine 240 and directlythrough the first pass of the heat exchanger 220. Upon exiting the firstpass, the bleed air then mixes at a mixing point with the recirculationair D2 provided by the fan 280 through the valve V6 to produce mixedair. The mixing point in this case can be downstream of the compressor244 and/or upstream of a second pass of the heat exchanger 220. Themixed air enters the second pass of the heat exchanger 220, where it iscooled by ram air to the temperature required by the chamber 202 toproduce cool air. The cool air then goes directly into the chamber 202via valve V7. Further, the chamber discharge air D1 is used to keep theair cycle machine 240 turning at a minimum speed. That is, the chamberdischarge air D1 flowing from the chamber 202 through the valves V4 andV5 enters and expands across the turbine 245, so that work is extracted.This work is utilized to turn the air cycle machine 240 at, for example,a minimum speed of approximately 6000 rpm. The air exiting the turbine245 is then dumped overboard through the shell 210.

The low pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 isapproximately 1 psi above the chamber pressure (e.g., conditions atcruise where altitudes are above 30,000 ft. and conditions at or nearstandard ambient day types).

In a boost pressure mode of operation, the bleed air from the inlet 201enters the compressor 244, where it is compressed and heated. Thecompressed and heated air from the compressor 244 passes through thefirst pass of the heat exchanger 220 and then mixes at a mixing pointwith the recirculation air D2 provided by the fan 280 through the valveV6 to produce mixed air. The mixing point in this case can be downstreamof the compressor 244 and/or upstream of a second pass of the heatexchanger 220. The mixed air enters the second pass of the heatexchanger 220, where it is cooled by ram air to the temperature requiredby the chamber 202 to produce cool air. The cool air then goes directlyinto the chamber 202 via valve V7. Further, the cabin discharge air D1is used to provide the energy to pressurize the bleed air entering thecompressor 244. That is, the chamber discharge air D1 flowing from thechamber 202 through the valves V4 and V5 enters and expands across theturbine 245, so that work is extracted. The amount of work extracted bythe turbine 245 is enough to turn the air cycle machine 240 at the speedrequired by the compressor 244 to raise a pressure of the bleed to avalue that can drive the bleed air through the heat exchanger 220 andinto the chamber 202.

The boost pressure mode can be used at flight conditions where thepressure of the bleed air entering the air cycle machine 240 is as lowas 2.5 psi below the chamber pressure (e.g., conditions at cruise wherealtitudes are above 30,000 ft. and conditions at or near standardambient day types).

Aspects of the embodiments are described herein with reference toflowchart illustrations, schematics, and/or block diagrams of methods,apparatus, and/or systems according to embodiments of the invention.Further, the descriptions of the various embodiments have been presentedfor purposes of illustration, but are not intended to be exhaustive orlimited to the embodiments disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the described embodiments. The terminologyused herein was chosen to best explain the principles of theembodiments, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the preferred embodiment to the invention had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

What is claimed is:
 1. A system of an aircraft, the system comprising:an inlet arranged in fluid communication with a bleed air source suchthat the inlet is configured to receive a flow of bleed air; acompressing device including a compressor having a compressor inlet, thecompressor inlet being fluidly connected to the inlet; and a heatexchanger being fluidly coupled to an outlet of the compressor, whereinthe heat exchanger includes a first pass and a second pass, both thefirst pass and the second pass being located downstream from thecompressor; and wherein an outlet of the first pass of the heatexchanger is directly connected to an inlet of the second pass via afirst conduit and the outlet of the first pass is fluidly connected toan inlet of the compressor via a second conduit such that a portion ofthe bleed air output from the first pass is returned to the compressorinlet via the second conduit.
 2. The system of claim 1, comprising: asecond inlet configured to receive a flow of recirculation air from arecirculation air source, the second inlet being fluidly coupled to theheat exchanger between the outlet of the first pass and the inlet of thesecond pass such that a mixture of recirculation air and bleed air isprovided to the inlet of the second pass of the heat exchanger.
 3. Thesystem of claim 2, wherein the recirculation air source is a pressurizedvolume of the aircraft .
 4. The system of claim 1, wherein the bleed airsource is an engine.
 5. The system of claim 1, wherein the heatexchanger is a ram air heat exchanger.
 6. A system of an aircraft, thesystem comprising: a first inlet arranged in fluid communication with ableed air source such that the first inlet is configured to receive aflow of bleed air; a second inlet arranged in fluid communication with arecirculation air source such that the second inlet is configured toreceive a flow of recirculation air; a compressing device arranged influid communication with the first inlet, the compressing devicecomprising a compressor having a compressor inlet and a compressoroutlet, wherein the compressor inlet is configured to receive the flowof bleed air from the first inlet; and a heat exchanger fluidlyconnected to the compressor outlet such that the flow of bleed airoutput from the compressor outlet is provided to the heat exchanger, theheat exchanger including a first pass and a second pass, both the firstpass and the second pass being located downstream from the compressingdevice; wherein the second inlet is arranged in fluid communication withthe heat exchanger at a location downstream from the outlet of the firstpass such that the flow of recirculation air is mixes with the flow ofbleed air output from the first pass at the inlet of the second pass ofthe heat exchanger.
 7. The system of claim 6, wherein the recirculationair source is a pressurized volume of the aircraft.
 8. The system ofclaim 6, wherein the bleed air source is an engine.
 9. The system ofclaim 6, wherein the heat exchanger is a ram air heat exchanger.